Hot metal coating process



M. SCHON HOT METAL COATING PROCESS May 2, 1939.

7 Filed Sept. 18, 1936 0M4. -r @MW Patented May 2, 1939 HOT METAL COATING PROCESS Matthew Schon, Baltimore, Md., assignor to Crown Cork & Seal Company, Inc., Baltimore, Md., a corporation of New York Application September 18, 1936, Serial No. 101,525

3 Claims.

This invention relates to a method for producing tin plate and is also useful in the manufacture of tin coated wire. Particularly, the invention is directed to a method whereby continuous 5 strips or lengths of steel may be provided with the desired tin coating.

One of the problems which confronts the industry and constitutes a source of considerable expense is the necessity for pickling, e. g., white pickling, the steel prior to its introduction into P the coating bath. The customary procedure of making tin plate consists in taking the stiff and spongy steel from the hot mills and first pickling the same to remove oxide. Thereafter, the steel 16 is annealed and rendered soft and is then subjected to a cold rolling. This latter step stiffens the steel and it'becomes necessary to give it a second annealing or softening treatment whereby full finish black plate is produced. Following 20 the second annealing, the customary procedure is to give the steel 9. further pickling to remove the oxide film produced by the two annealings, as well as due to exposure of the sheet. Usually this second or white pickling is brief, but heretofore has been regarded as absolutely necessary, and after it has been performed, the sheets are submerged in acidulated water in which they remain until fed to the tinning pot.

I have discovered that the necessity for a sec- 0nd pickling step, as well as the use of an acid or bash treatment, are not required for the manufacture of tin plate if certain preliminary conditions are carried out, and which conditions furthermore enable lengths or strips of steel to be prepared for the timing operation and tinned in a continuous manner at a relatively high temperature. The product obtained is superior to the usual tin plate and the method is rapid and affords a very marked economy.

Thus I proceed, following the usual cold rolling operation mentioned above, by passing the wire or strip continuously through an annealing furnace where the steel is given a bright anneal and then cooled, so that, at its point of exit from the annealing furnace, the temperature is about 400 C. The exit end of the annealing furnace is disposed below the level of the tinning bath and sealed thereby, and the annealing furnace is provided with a non-oxidizing atmosphere, preferably a reducing atmosphere so as to preclude any possibility of oxidation on the one hand and remove any oxide on the other. The strip or wire is continuously carried through the usual tinning pot in which the tin is maintained at a temperature of about 580 to 590 F. and without emerging from the oil bath, the length of steel is continuously moved through a washer" containing a very weak solution of alkali which cools the steel and removes most of the oil. Thereafter, the strip may be passed through branner and 10 bufilng rolls as desired. No second or white pickling followed by acid treatment is necessary, so that these objectionable and expensive operations incident to present methods are omitted; in addition, my invention enables a continuous 16 method to be utilized. The tin pot with associated oil bath and washer" while well know, heretofore have only been used in the manufacture of tin plate in the form of sheets of relatlvely short length, but I find, that by means of 10 my invention, they are capable of inclusion in a continuous method and enable a rapid production of a very high quality tin plate to be obtained.

The product of the present invention is useful in the manufacture of tine cans and metal con- 25 tainers and also metal caps of various types. In the accompanying drawing, I have 'illustrated one apparatus for carrying out the continuous method, but it will be appreciated that other constructions may be utilized in pursuance of the invention.

The numeral l0 indicates a coil of metal strip such as thin steel of a gauge usually employed in the manufacture of tin plate, but as stated heretofore, the method and apparatus may be 35 utilized in connection with wire. The strip I0 is continuously passed over idler roll ll into the heating leg I! of an annealing furnace and over the roller l3 downwardly through the cooling leg H of the furnace. The temperature maintained within the furnace is such that the steel will be given a brightanneal and will be cooled in the leg It to a temperature of substantially 400 C. for presentation to the tin bath having a temperature of about 580 F. to 590 F. The annealing is preferably conducted in the presence of a non-oxidizing atmosphere, usually a reducing atmosphere such as hydrogen, and the leg I4 is so disposed with relation to the metal bath l5 that the lower end N5 of the leg will be disposed below the level of the bath and sealed thereby. In this manner, the strip is continuously annealed without opportunity for oxi-- dation and its lower end is sealed against exposure to oxidizing influences by reason of the 66 entrance of emersion of the lower end of the leg It in the ,ba

The speed, i movement of the strip through the annealing furnace and the temperature thereof are controlled to produce the required annealing and obtain the desired reduced temperature and the temperature of the bath, and the rate of movement of the strip therethrough is likewise controlled so that a coating of proper thinness is formed on the strip.

The strip is then continuously carried from the metal bath through the usual oil bath ll of palm oil having a temperature ot .about 560 F. having a lower temperature and between a pair of rolls I8 to produce a. thin, evenly distributed, smooth tin coating; then through a washer IQ of a suitable weak solution of alkali having a further reduced temperature, whereupon the cooled sheet is submitted to suitable polishing rolls 20 or branner and bufflng rolls if desired and continuarmour The tin plate has a lustrous surface and the uct for use in the manufacture of metal containers and closures, e. g., lug, screw, and crown caps.

The term "black plate" referred to in the ap- 5 pended claims is intended to include wire, sheets and continuous strips of steel which have not been given the customary second anneal, i. e., the steel after the first pickling, and annealing, and cold rolling. 10

I claim:

1. The method of making tin plate which consists in annealing black plate in a reducing atmosphere, cooling the same in a reducing atmosphere, and then without permitting the plate to 15 be exposed to oxidizing influences, directly in-\ troducing the plate into a tinning bath, and coating the same with tin.

2. The method in accordance with claim 1 in which the plate is cooled to a temperature of sub- 20 stantially 400 C.

ous strip.

MATTHEW SCHON. 2 

